Using an AC1200 ext. to push my wifi to my shops AC750,4 bars fast. Looses connection nightly why?

Ok as stated AC1200 from Adsl router receiving 5 bars.

the 1200 pushes the wifi 300feet to my shop across a empty part of the yard.

the shop has lots of metal and wifi inside was impossible, however 4 bars outside.

purshed a AC750 that takes that 4bars through a window and puts it Back to hard wire to my shop pc. (Cat5). This works great with only a .4 g loss with speed test. Stream and back feed an I.P. Camera great.

so connection awesome but disconnects most nights.

can anyone recommend some settings to keep the connection more perminant?

thanks :)

Tony